GB2025015A

GB2025015A - Apparatus for and method of making pitch fibre infusible

Info

Publication number: GB2025015A
Application number: GB7922630A
Authority: GB
Original assignee: Kureha Corp
Current assignee: Kureha Corp
Priority date: 1978-06-30
Filing date: 1979-06-29
Publication date: 1980-01-16
Also published as: CA1126918A; US4283369A; DE2925950B2; FR2429849A1; JPS5853085B2; US4265869A; GB2025015B; DE2925950A1; DE2925950C3; JPS556547A; FR2429849B1

Description

1 GB 2 025 015 A 1

SPECIFICATION

Apparatus for and Method of Making Pitch Fiber Infusible The present invention relates to an efficient method of and apparatus for producing carbon fiber by making infusible and carbonizing pitch fiber which is obtained by melt-spinning petroleum-tar pitch 5 or coal-tar pitch.

In the production of carbon fiber by melt-spinning petroleum-tar pitch or coal-tar pitch, it has been known that pitch fiber obtained is subjected to a reaction to make it infusible prior to the carbonizing thereof. The pitch fiber is made infusible as it is subjected to a take-up system in which the pitch fiber is fed and taken up around a roll, or a net conveyor system in which the pitch fiber is placed on and transferred by a net conveyor. However, in the take-up system, a high productivity cannot be 10 obtained since the pitch fiber cannot be taken up at a high rate due to the low physical strength and ductility thereof. Moreover, it takes much time to mend pitch fiber when it is broken during the reaction according to this system. In the net conveyor system, the pitch fiber is waved in the form of a net and the density of the fiber is increased by the force of gravity (their own weights). This causes the fiber to be locally damaged, and the fiber as a whole is not sufficiently oxidized.

An object of the present invention is to eliminate the above-mentioned drawbacks encountered in the prior art method of this kind.

Another object of the present invention is to provide a method of making pitch fiber infusible in an excellent manner at a high producitivity.

Still another object of the present invention is to uniform the flow rate of a circulation gas in a 20 tray by setting to a level in a suitable range the ratio of the packing density of -pitch fiber suspended in the tray to the superficial velocity of the circulation gas in the tray.

A further object of the present invention is to provide an apparatus for making pitch fiber infusible, which permits increasing the productivity of pitch fiber and producing excellent infusible pitch fiber.

According to one aspect of the present invention, there is provided a method of making pitch fiber infusible in an air atmosphere containing NO,, at an elevated temperature in the production of carbon fiber by making infusible and carbonizing pitch fiber which is obtained by melt-spinning petroleum-tar pitch or coal-tar pitch, the method comprising placing bars across an upper portion of a cross sectionally U-shaped tray, suspending pitch fiber from the bars, introducing the resulting tray into an 30 infusible material producing furnace having gas exchanging chambers in the inlet portion and outlet portion thereof as well as at least two gas circulating means each of which comprises a combination of a blower or a fan and a heat exchanger, and retaining the tray in said furnace.

According to another aspect of the present invention, there is provided an apparatus for making pitch fiber infusible, which comprises an infusible material producing furnace capable of holding a 35 plurality of cross-sectionally U-shaped trays each of which has bars placed across an upper portion thereof with pitch fiber suspended therefrom the furnace having at least two gas circulating means each of which comprises a blower or a fan and a heat exchanger and each of which is for use in circulating an atmospheric gas to cool the reaction zone, as well as gas exchanging chambers adjacent to the inlet portion and outlet portion thereof.

The above and other objects as well as advantageous features of the invention will become clear from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.

Fig. 1 is a perspective view of a tray used in the present invention, which has bars placed across the upper portion thereof with pitch fiber suspended therefrom; and Fig. 2 is a schematic diagram of an apparatus according to the present invention for making pitch fiber infusible.

A cross-sectionally U-shaped tray 2 used in the present invention has four side walls 2a, 2a, 2b, 2b and a bottom wall 2c which are made of metal net with the upper portion thereof opened as shown in Fig. 1. A plurality of bars 3 are placed across the opened portion of the tray 2, and tvro pitch fiber 1 50 of 10-30 mm in diameter, which is obtained by melt-spinning petroleum-tar pitch or coal-tar pitch, is suspended from the bars 3. The tray 2 with the pitch fiber 1 suspended from the bars 3 is introduced into an infusible material producing furnace 4 as shown in Fig. 2, so as to allow the pitch fiber 1 to be treated as will be described later. The metal net prevents the pitch fiber 1 from contacting, for instance, the wall of the furnace and so deforming, while ensures passing the circulation gas caused by a 55 circulating means hereinafter mentioned.

The furnace 4 for making materials infusible shown in Fig. 2 consists of a known furnace of this kind, which has been improved with a view to achieving the objects of the present invention. The furnace 4 is capable of holding a plurality of trays 2 and has gas exchanging chambers 5, 6 adjacent to the inlet portion and outlet portion thereof to prevent the composition and temperature of the atmospheric gas in the furnace from being varied when the trays 2 are inserted therein and withdrawn therefrom.

The furnace 4 is constructed such that the atmospheric gas therein has gradually increasing temperatures from the inlet portion thereof toward the outlet portion thereof. The furnace 4 is further 2 GB 2 025 015 A 2 provided with blowers or fans 7 which are suitably spaced from one another, and at least two (four in this embodiment) gas circulating means 9 for use in withdrawing the atmospheric gas from a lower portion of the furnace and feed thereinto from an upper portion thereof to thereby produce vertical currents of the atmospheric gas. Each of the gas circulating means 9 has a heat exchanger 8 therein to remove the heat generated during a reaction for making pitch fiber infusible, and thereby maintain constant the temperature of the atmospheric gas in every part of the furnace.

According to the method of the present invention, a tray 2 with pitch fiber 1 suspended from bars 3 as shown in Fig. 1 is introduced into an infusible material producing furnace 4 as shown in Fig. 2, and intermittentlytransferred in an air atmosphere of 100-4001C containing 0. 1-10 volume percent of 10 N021 to make the pitch fiber 1 infusible in 1-4 hours.

The amount (packing density) of pitch fiber 1 suspended in the tray 2 can be arbitrarily varied by changing the suspension intervals. When the amount of pitch fiber 1 is too small, the productivity may be lowered. When the amount of pitch fiber I is too large, the reaction for making the pitch fiber infusible may not be uniformly carried out and the atmospheric gas may not flow uniformly during a carbonizing reaction to be conducted thereafter.

This causes the temperature inside the tray 2 to be varied in each part thereof. The amount of pitch fiber 1 is preferably 1-30 kg/cM3 and, more preferably, 2-20 kg/ml.

The pitch fiber suspended in a tray and introduced into an infusible material producing furnace to make the pitch fiber infusible is in the form of a tow. Then, when the pitch fiber of a packing density of over 1 kg/m' is treated with a natural convection of air, a heat removing gas does not flow uniformly in 20 the tow. Accordingly, the heat cannot be removed satisfactorily so that the temperature is varied in each part of the inside of the tow. This causes the physical properties of finished fiber, which is obtained by carbonizing fiber subjected to an infusible material producing reaction, to be varied. In addition, a violent proceeding of a reaction occurs.

In order to prevent the above-mentioned inconveniences, the infusible material producing furnace 25 4 is provided with gas circulating means 9 each of which has a fan 7 whereby the reaction heat is removed by forced convection into the reaction zone as described above. The furnace 4 is further provided with gas exchanging chambers 5, 6 adjacent to the inlet portion and outlet portion thereof to prevent the composition and temperature of the atmospheric gas in the furnace from being varied when the trays are inserted therein and withdrawn therefrom.

The infusible material producing furnace has an air atmosphere of 1004001C containing 0.110 volume percent of NO,, and pitch fiber is detained in the furnace for 1-4 hours to make the same infusible. The conditions restricted here are the same with those that are generally adopted in making the pitch fiber infusible.

In order to practice the present invention, a tray 2 with pitch fiber 1 suspended therein is first 35 introduced into a gas exchanging chamber 5 in which the atmospheric gas is completely exchanged so that the atmospheric gas is rendered identical with the atmospheric gas in the infusible material producing furnace, and the tray is then introduced into the furnace. Consquently, the temperature of the inside of the furnace is not decreased and the composition of the atmospheric gas is not varied.

Namely, the pitch fiber 1 can be made infusible uniformly under preferable conditions.

As the reaction for making pitch fiber infusible is progressed, the temperature is increased due to the reaction heat so that the temperature is possibly varied in each part of the inside of the tray. The variation of temperature may be arbitrarily regulated while producing downward current of the atmospheric gas in the tray 2 by blowers or fans 7, to remove the heat with heat exchangers 8. Since the heat removing effect can be improved by regulating the flow rate of the circulation gas, it is 45' possible to reduce the difference between the softening point of pitch fiber and the temperature of the atmospheric gas. This permits the pitch fiber to be made infusible in a short period of time. It is preferable that the circulation gas for use in removing the heat flow in a downward direction. If the gas flows in an undesirable direction, the suspended pitch fiber may be curled up or entangled due to the light weight thereof. This prevents the reaction heat from being removed in a satisfactory manner.

Then, a circulation gas flowing downwardly is the most helpful to prevent disorderly movements of the pitch fiber.

When the superficial velocity of the circulation gas in a furnace is too high, the load of a motor may be increased, and the reaction may not be carried out economically. Therefore, the ratio of the packing density (kg/ml) of pitch fiber in the form of tow to the superficial velocity (Nm/sec) of the 55 circulation gas in a furnace is regulated such that the ratio satisfies the following formula.

Packing density of pitch fiber 50> >10 Superifical velocity of circulation gas in a furnace It is necessary to increase the superficial velocity of circulation gas in a furnace when the packing density of pitch fiber is high. However, an excessively high superficial velocity of circulation gas in a furnace as compared with the packing density of pitch fiber causes to prevent the reaction from being 60 i z 4 3 GB 2 025 015 A carried out economically and also causes pitch fiber to be broken in some cases to raise trouble in the processing step.

On the contrary, when the superficial velocity of circulation gas in a furnace is low as compared with the packing density of pitch fiber, the heat-removing gas does not flow uniformly so that the temperature of the pitch fiber is varied in each part thereof. This causes not only the variation in the physical properties in each part of carbonized fiber but also the violent proceeding of the reaction. A preferably superficial velocity of circulation gas is 0.05-2.0 Nm/sec. In other words it is preferable to operate the furnace at a superficial velocity of circulation gas of a level in the above range and satisfying the formula shown above.

When the temperature of the infusible material producing reaction is closer to the softening point10 of pitch fiber, the reaction may be carried out in shorter period of time. However, when the reaction temperature is too close to the softening point, it becomes difficult to locally suppress the reaction, and a violent proceeding of a reaction may occur.

On the contrary, when the difference between the reaction temperature and the softening temperature of the pitch fiber is too large, the reaction time becomes long. This makes it necessary to 15 increase the dimensions of the reactor to a considerable extent. A preferable reaction temperature is lower than the softening point of pitch fiber by 5-501C.

When pitch fiber having a softening point of around 1 651C, which is made from a polymerized pitch obtained by heat-treating, for example, naphtha tar, is subjected to an infusible material producing furnace, a preferable reaction temperature at the Inlet portion of the furnace is 160 11 50C. In this case, it is recommendable to increase the reaction temperature so that the difference between the reaction temperature and the softening point, which is gradually increased as the reaction progresses, of the pitch fiber may become substantially constant, until the softening temperature has attained around 3000C. However, it is preferable to regulate the reaction temperature so that it may not be over 3501C and, more preferably, not over 3001C. When the reaction temperature is extremely 25 high, a reaction for polymerizing the pitch fiber may occur in addition to the reaction for making the pitch fiber infusible. This causes to produce carbon fiber, a final product, having low physical strength and ductility.

According to the present invention, trays with pitch fiber suspended therein are introduced in order into an infusible material producing furnace via a gas exchanging chamber 5, and the trays in the 30 front portion of the furnace are thereby intermittently transferred as they are subjected to an infusible material producing reaction. The trays are forced out into a gas exchanging chamber on the side of the outlet when the reaction has been completed. Then, the trays are withdrawn from the gas exchanging chamber while shutting off the chamber against the furnace body so that no outer air may enter the furnace body. The pitch fiber is then carbonized in a carbonizing furnace to be turned into carbon fiber 35 products.

Example 1:

In each of trays of 1.2 m in height and 1.44 M2 in sectional area as shown in Fig. 1 was suspended 7.0 kg of pitch fiber obtained from naphtha tar. The resulting trays were introduced into an infusible material producing furnace as shown in Fig. 2, which is capable of holding 14 trays. These 40 trays were introduced one by one every 17 minutes into an air atmosphere in the furnace of 100 2501C containing 1.0 volume percent of NO., and each tray was withdrawn from the furnace 4 hours after it had been introduced thereinto. As a result, excellent infusible pitch fiber was obtained. During the above reaction, the superficial velocity of the circulation gas in a furnace 0.25 Nm/sec.

Example 2: 45

The same infusible material producing reactions as in Example 1 were conducted with varying the packing density (p) of pitch fiber, the difference (At) between the softening point of pitch fiber and reaction temperature and the superficial velocity (Ug) of circulation gas in a furnace, in an air atmosphere of 100-2501C containing 1.0 volume percent of N02. The results of these reactions are shown in the following table as Example No. A-D. The reaction time required for these Examples A- 50 D is also shown in the table.

Example 3:

The same infusible material producing reaction as in Example 1 was conducted in an air atmosphere of 100-2501C containing 5.0 volume percent of NOThe result of this reaction is shown in the table as Example No. E. 55 The same reactions were conducted as Comparative Examples F. G under the same conditions except that p, At and Ug were further changed. The reaction time required for these reactions will also be shown in the table below.

4 GB 2 025 015.A 4.

Table

Reaction Example No. p(kglml) Llg(NmIsec) At(OC) time(h) A 4.0 0,13 40 4.0 B 4.0 0.20 25 3.0 c 4.0 0.33 15 1.8 D 10.0 0.50 25 3.0 E 18.0 0.50 25 2.0 F 2.0 0.03 40 7.0 (Comparative Example)

G 10.0 0.20 50 8.2 (Comparative Example)

15, The present invention 1 not, of course, limited to the above embodiments; it may be modified in 15 various ways within the scope of the appended claims.

Claims

1 - Apparatus for use in the infusibillsation of pitch fiber which comprises a furnace capable of holding a plurality of trays adapted for suspension therein of pitch fiber, said furnace having at least two gas circulating means, each of which incorporates a heat exchanger and is adapted to circulate the 20 gases within the furnace and thereby remove heat generated by the infusibilisation reaction during use of the apparatus, and respective gas exchanging chambers at the entrance to and exit from the furnace.

2. Apparatus according to claim 1 wherein each gas circulating means includes a blower or a fan.

3. Apparatus according to claim 1 or 2 wherein said gas circulating means are arranged along the length of the furnace and are adapted to control the temperature inside the furnace such that it 25 increases from the entrance to the exit thereof during use.

4. Apparatus according to any one of the preceding claims wherein said gas circulating means are adapted to provide vertical downdraughts within the furnace.

5. Apparatus for use in the infusibilisation of pitch fiber substantially as hereinbefore described with reference to and as illustrated by Figure 2 of the accompanying drawing.

6. Apparatus as claimed in any one of the preceding claims which is loaded with a plurality of trays adapted for suspension therein of pitch fiber.

7. Apparatus according to claim 6 wherein each tray is approximately Ushaped in cross-section and has bars positioned across an upper portion thereof.

nets.

8. Apparatus according to claim 7 wherein the sides and bottom of the trays are made of metal

9. Apparatus according to claim 6 wherein each tray is substantially as hereinbefore described with reference to and as illustrated by Figure 1 of the accompanying drawings.

10. A method of infusibilising pitch fiber which comprises suspending the pitch fiber in a tray therefor and introducing loaded tray into a furnace containing air and NO, and comprising at least two 40 gas circulating means, each of which incorporates a heat exchanger and circulates the gases within the furnace thereby to remove heat generated by the infusibilisation reaction, and respective gas exchanging chambers at the entrance to and exit from the furnace.

11. A method according to claim 10 wherein the pitch fiber has been obtained by melt-spinning petroleum-tar pitch or coal-tar pitch.

12. A method according to claim 10 or 11 wherein the tray is approximately U-shaped in crosssection and has bars positioned across an upper portion thereof.

13. A method according to claim 12 wherein the sides and bottom of the tray are made of metal nets.

14. A method according to any one of claims 10 to 13 wherein said gas circulating means each 50 include a blower or a fan.

15. A method according to any one of claims 10 to 14 wherein said gas circulating means are arranged along the length of the furnace and control the temperature inside the furnace such that it increases from the entrance to the exit thereof.

16. A method according to any one of claims 10 to 15 wherein said gas circulating means 55 provide vertical downdraughts within the furnace.

17. A method according to any one of claims 10 to 16 wherein the packing density of said pitch suspended in said tray and the superficial velocity of the gas circulated by said circulating means in said furnace are regulated such that:

50> - Packing density of pitch fiber >10 60 Superficial velocity of circulation gas in a furnace R GB 2 025 015 A 5

18. A method according to any one of claims 10 to 17, wherein the superficial velocity of the gas circulating in the furnace is from 0.05 to 2.0 Nm/sec.

19. A method according to claim 10 substantially as hereinbefore described with reference to any one of Examples 1 to 3.

20. A method of infusibilising pitch fiber substantially as hereinbefore described with reference to 5 Figures 1 and 2 of the accompanying drawings.

2 1. Carbon fibers which have been prepared form infusibilised pitch fiber produced by a method as claimed in any one of claims 10 to 20.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1980. Published by the Patent Office, 2 5 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.

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